Editing Thorp, Washington (section)

===Topography===
North and northeast of the town of Thorp along the Yakima River channel is the gradual upward lift of the Thorp Drift, marked by an elevation change due to the incline onto the terminal [[moraine]] that marks the furthest advance of the Thorp [[glacier|Glacial]] stage. Here the Thorp [[Gravel]]s, which are named for the town of Thorp and the Thorp Glacial episode, are exposed along the ancient river channel in what is known as the "Slide Area". The gravels were formed at the terminus of the Thorp Glacial advance approximately 600,000 years ago.<ref name="waitt">Richard B. Waitt, Jr., ''Late Cenozoic Deposits, Landforms, Stratigraphy, and Techtonism in the Kittitas Valley, Washington'', U.S. Geological Survey, Professional Paper 1127, Washington DC: Government Printing Office (1979) pp. 9.</ref><ref>Eric S. Cheney, ''Regional Tertiary Sequence Stratigraphy and Regional Structure on the Eastern Flank of the Central Cascade Range, Washington'', Vol. 4, Geological Society of America, (GSA Field Guides, 2003) pp. 177-199.</ref>

The Thorp Gravels themselves are believed to be between 3 and 4 million years old. The whole structure is composed of individually layered belts of gravel and [[sand]] which are not well consolidated, continually weather, and are prone to continuing [[erosion]] and [[landslides]] averaging 30 degrees. The area is rich with wildlife, including [[bald eagle]]s and [[osprey]] who hunt for prey along the river. It is also a crossing point for [[deer]] and [[elk]] who often can be seen at dawn and dusk heading to the river for water.<ref name="jones">Jana Jones Mabry, ''Field Trip Guidebook to the Natural History of Kittitas County'', Ellensburg, Washington: Central Washington University, pp. 44.</ref><ref name="waitt"/>

About {{convert|7|mi|0}} west of Thorp, the first glimpses of the [[Columbia River]] Plateau are seen where the Yakima River has cut into the westernmost edge of the basalt [[plateau]]. The [[Columbia Plateau]] basalt formed when [[lava]] poured out of [[fissure vents|fissures]] in the ground across [[eastern Washington]] during the Miocene era, 17 to 20 million years ago, erupting intermittently for over 10 million years.  Many layers of basalt successively flowed over one another, back when the area was still flat.<ref>Charles D. Lenfesty and Thomas F. Reedy, ''Soil Survey of Yakima County Area, Washington'', Soil Conservation Service (1985).</ref> Subsequent to the Miocene lava flows, the [[volcanoes]] of the [[Cascade Mountains]] actively [[volcanic eruption|erupted]], depositing [[volcanic ash|ash]], cinders, [[pumice]] and [[lahar|mudflows]] that eventually inter-fingered with the alternating basalt layers throughout the region.<ref>Mac McCulloch, ''Gateway to Time: Mile by Mile Guide to the Yakima Canyon'', Yakima, Washington: Shields Printing (1990).</ref>
{{climate chart
| Thorp, Washington<ref>[http://climate.fizber.com/washington-city-thorp-climate.html Fizber, Thorp Climate] {{Webarchive|url=https://web.archive.org/web/20120329134649/http://climate.fizber.com/washington-city-thorp-climate.html |date=2012-03-29 }} (Retrieved 2011-10-06)</ref>
|16.5|34.3|7.94
|25.2|37.8|6.40
|26.5|42.2|5.41
|31.1|48.9|0.97
|37.8|61.6|1.24
|44.2|65.4|1.35
|51.8|77.2|0.07
|48.3|72.2|0.11
|43.6|67.2|0.44
|34.4|52.6|4.64
|28.5|42.5|5.31
|25.5|35.9|9.06
|units = imperial
|float = left
|clear = both }}

Interstate 90 drops through the Thorp Drift, which marks the oldest and furthest reaching known glacial moraine in the Kittitas Valley. Changes in the types of [[vegetation]] become more evident in this area. The changes are the result of a drop in elevation of about 1,400&nbsp;feet from the summit of [[Snoqualmie Pass]] to Thorp, and a significant drop in [[precipitation (meteorology)|precipitation]] of about 107&nbsp;inches average a year at the [[summit (topography)|summit]] of Snoqualmie Pass, to 42.94&nbsp;inches average a year at Thorp.<ref name="jones"/><ref>Stephen P. Reidel, Vernon G. Johnson and Frank A. Spane, ''Natural Gas Storage in Basalt Aquifers of the Columbia Basin: A Guide to Site Characterization'', Richland, Washington: Pacific Northwest Laboratory (2002) pp. 44.</ref>

At the bottom of the Thorp Drift moraine the view opens up into the Kittitas Valley which is deeply buried in river gravel deposited by the [[ancient]] Yakima River. This valley is a [[syncline]] that creates the Ellensburg Basin located between [[Mission Ridge Ski Area|Mission Ridge]] to the north and [[Manastash Ridge]] to the south. The Ellensburg Basin, more formally called the Ellensburg [[geological formation|Formation]], holds nearly 4,000&nbsp;feet of rock, sand, and gravel that accumulated over a period of 2 to 10 million years during the Miocene and lower [[Pliocene]] age.<ref name="jones"/><ref>Richard B. Waitt, Jr., ''Shorter Contributions to Stratigraphy and Structural Geology'', U.S. Geological Survey, Professional Paper 1126-A-J, Washington DC: Government Printing Office (1979), pp. H-54.</ref>